cpdup: multiple bug fixes regarding file flags

I've posted patches for two bug fixes for cpdup to the bug tracker.
The first fixes handling of the UF_ARCHIVE file flag for destination
filesystems that support it. It's mostly relevant for downstream
consumers of cpdup like FreeBSD. The second fixes deleting
directories that have certain file flags set. It's relevant for
Dragonfly and all cpdup consumers. Could somebody please review these
patches?